General Prior Art Packing Devices
In packaging bottles, cans and other such containers, it has been known to assemble the containers into cardboard trays and to provide a transparent film around the trays and containers, which allows for identification of the containers while packaged. However, this packaging configuration is disadvantageous in that it necessitates the use of film on the bottom of the trays, which is not only wasteful, but also creates problems if further processing of the trays includes frictional sliding contact on the bottom of the trays.
Therefore, it has been known to provide packaging machines which apply a sheet of film over the top of the containers, and weld the film to side walls of the trays. Such a packaging machine is disclosed in U.S. Pat. No. 3,890,763 issued on June 24, 1975, to Ullman, and incorporated herein by reference. The packaging machine there illustrated and described, a high speed WRAPCAP machine, includes a conveyor for moving a series of rectangular corrugated paperboard trays along a predetermined path. Arranged in succession along the path are a first glue station, a turning station, a film disposing station, and a compression station. At the first glue station glue applicators are provided on opposite sides of the path for applying a stripe of adhesive on the outside walls of each tray. The turning station rotates the tray through a right angle so that the trays then advance with the adhesive stripe on the leading and trailing walls. Additional glue is then provided on the other opposite walls of each tray. At the film supplying station a supply of film, for examplel of polyvinyl chloride, polypropylene or polyethylene, is provided. As the tray moves through the film disposing station, the film sheet material is drawn over the top of the tray by a plurality of flight bars commonly driven along an orbital path. The flight bars press the film against the adhesive stripes on the trays, and the adhesive then bonds the film to the tray. Cutting blades are provided in cooperative relation with the the flight bars for piercing and separating the film sheet material between trays. After the sheet has been cut, the tray is then released and discharged from the compression station. The tray then moves on a downwardly inclined conveyor to be conveyed to a heat shrink tunnel. In the shrink tunnel, the heat shrinking of the sheet brings its unbonded side portios into contact with the second pair of adhesive stripes to form a bond. Additionally, spring-loaded rollers are provided at opposite sides of the shrink tunnel exit to flatten out rough ears of the sheet and to press the side portions of the sheet against the adhesive to form a better and more attractive bond.
Although machines as described above are effective, they possess a number of disadvantages, one being that the machines are limited to processing a fixed package size, as the flight bars are all fixed to one pair of drive chains.
U.S. Pat. No. 4,365,456, issued on Dec. 28, 1986, to Ullman, and herein incorporated by reference, discloses an adjustable WRAPCAP packaging apparatus including two independently movable sets of flight bars, which allow the apparatus to be adjusted to accommodate packages of different sizes over a range within the limits of the machine. The method of adhering plastic film disclosed in the '456 patent includes placing the film over the tops of the packages, pressing the film sheet against the front and rear walls of the package, and while so compressed heating the film for a sufficient length of time to weld the film sheet to the walls of the package, and then releasing the heat and pressure.
Although the adjustable WRAPCAP machine is effective in accepting a plurality of tray sizes, its capacity is limited in that it may only maintain one package in compression at one time, unlike the high speed WRAPCAP device previously discussed.